U.S. Pat. No. 6,361,275 (Wobben) discloses a wind turbine, wherein the pitch angles of each wind turbine blade can be adjusted independently such that corrections for varying wind speeds in the swept area of the wind turbine blades can be made. The wind speed often increases with the distance to the surface of the ground and it may thus be advantageous to adjust the lift power of the blades such that the load on the blade is substantially uniform during its entire rotation. However, this solution may also be used to compensate for other types of variations in the wind speed in the rotor plane.
The wind turbine according to U.S. Pat. No. 6,361,275 is, however, encumbered by the drawback that the adjustment cannot be made particularly fast, the conventional pitch hydraulics of the blade being used for this purpose. The hydraulics is not adapted for fast and almost instantaneous movements since a wind turbine blade, whose dead load may exceed 10 tons, has a comparatively large inertia.
As mentioned above, particularly at large wind turbines, eg offshore wind turbines, the wind speed may vary greatly locally in the area swept by the rotor. The rotor may have a diameter of more than 120 metres for which reason the wind speed may vary greatly due to local wind gusts and turbulence both in height and width.
In WO 97/01709 (Bonus Energy A/S) reference is made to wind turbine blades with active, adjustable flaps for changing the aerodynamic properties of the blade.
U.S. Pat. No. 4,692,095 relates to a wind turbine blade according to the background of the present disclosure.
According to a first aspect, the object of the invention is to provide a wind turbine blade of the modern, aerodynamic type with improved regulating properties to enhance the adjustment of the wind turbine to various wind conditions.